Google Maps API V3 not equal to Google Maps site on distance between two zipcodes

I have put together some code to calculate distances between two zip codes. When I enter the zip codes through the API I get a different distance than I do with the actual Google Maps site.

Anyone have an idea on why this is occurring?

A few ideas I have are:

• I am not centering to the zip code -> I was looking around to see how I could do this but no luck.

• The Google map开发者_如何学Gos site is including additional options that I am missing

• Issue with United Kingdom zip-codes -> read an old article stating that the UK has a strict requirement, not sure about this one.

The values I am testing are:

• Origin: le17 6qt United Kingdom
• Destination: Le16 9ul United Kingdom

Here is my code: http://www.pastie.org/883475

Here is an example page: djintelligence.com/quote/distance.asp